Stereophonic microphone



1968 MOTOYOSHI NAKANISHI 3,413,415

STEREOPHONIC MICROPHONE Filed June 16, 1965 F/gt/ INPUT INPUT 71 -TRANSISTORS OUTPUT -0UTPUT COMMON INVENTOR.

United States Patent 3,413,416 STEREOPHONIC MICROPHONE Motoyoshi Nakanishi, 1-511 5-ch0me, Honcho, Funabashi-shi, Chiba Prefecture, Japan Filed June 16, 1965, Ser. No. 464,295 Claims priority, application Japan, June 19, 1964, 39/ 34,595 11 Claims. (Cl. 179-1) ABSTRACT OF THE DISCLOSURE A stereophonic microphone comprising, substantially, a pair of sonic receptors, each having a vibrating plate disposed between an opposed pair of electrode plates adapted to be applied with voltages of opposite polarity with respect to each other. The pair of sonic receptors are combined in a unit, so that sounds from central sources facing the microphone are emitted as signal voltages of the center sounds by way of the two vibrating plates and sounds from sources left and right to the microphone are emitted as signal voltages separately of the left and the right sounds by way of the two pairs of electrode plates.

This invention relates to a novel and virtual stereophonic microphone, in general, and to a localization-ofsound type microphone which can efficiently perceive the direction of sound sources in ternary arrangement and can convert original sounds into ternary signals to reproduce sounds faithful to the original sounds, in particular.

The public interest in the stereophonic reproduction of sound has increased enormously in recent years. Up to the present time, a typical method of stereophonic reproduction of sound has been based on two channel system (two wave system), wherein two or more microphones are provided so that the microphones respectively receive sound waves emitted in different directions from sound sources. In this case, each sound obtained from the output signals of the respective microphones is virtually monophonic. A sound obtained by combining the monophonic output signals is usually called stereo. However, this is not true or virtual stereophonic sound. In sounds reproduced by a conventional stereo microphone, localization of sounds is inaccurate except when sound sources are on the right or on the left to the microphone.

Theoretically, an ideal stereophonic reproduction of sound consists in reproducing sound with stereophonic features from original sound to achieve the effect of localization of sounds. In other words, it is highly desirable that original sounds of central sources are reproduced to sounds at central position according to their locations and in a similar manner, original sounds of the right or left sources are reproduced to sounds at the right or left position. There have been few theories that elucidate the function of the auditory nervous system on localization of sounds when stimuli reach both ears. However, the following facts could be stated from our experiences. Both ears working together can localize the direction of original sound sources arranged in ternary fashion. Human ears can perceive the locations of sound sources arranged in ternary or spatial manner in our environment, that is, the relationship among sound sources which are respectively located at the left, the middle and the right with respect to the cars by hearing the sounds themselves. These could be explained by the fact that the human auditory nerves are endowed with an ability perceiving the location of sound sources by receiving sound waves, that is, the function of localization of sounds.

As mentioned previously, man owes it to localization of sounds that the human ear can perceive the direction of sound sources in ternary arrangement. An explanation being made according to the principle, that the eardrum is vibrated by sound Waves to cause voltage variation on the receptor organ of each ear. This voltage variation in each ear is coupled together by the auditory nerves to cause voltage differential, which is arranged in the nervous system and judged in a part of the brain as stereophonic sounds to thereby achieve localization of sounds. In this way, a primary factor for localization of sounds consists of the property of sound waves received from sound sources and man having a pair of the auditory organs on both sides of his head. A sound receiving system corresponding to the human auditory organ and a transducing system working together with the receiving system are necessary to reproduce a stereophonic sound in the true sense of the word which is different from the conventional word, stereo from original sounds. A stereophonic sound reproducing apparatus must comprise the mechanism which has the function to receive sound waves and convert them into stereophonically arranged signals. Giving further description, the minimum requirements are that a pair of sonic receptors can receive sound Waves from sources of original sounds and can convert sounds carried from the right, middle and left directions into stereophonically arranged signals for reproducing stereophonic sounds in order to achieve the effect of localizing the respective sounds. In other words, it is required that sounds are reproduced at the right side of the apparatus from right original sounds, sounds at the middle of the apparatus from a middle sound, and sounds at the left from left sounds.

On the contrary, in case of employing a conventional stereo device, stereophonic sounds in the true sense of the word cannot be obtained, and in this case, especially, a middle sound cannot be localized well because the sound which has been called stereophonic is obtained by only combining monophonic output signals.

It is one object of the present invention to provide a stereophonic sound reproduction in the true sense of the word by means of converting sounds into ternary or stereophonically arranged output signals in order to realize stereophonic broadcasting and stereophonic recording which have never been realized by any conventional stereo reproduction systems.

It is another object of the present invention to provide a novel stereophonic microphone having a function similar to that of the human auditory organ.

It is still yet another object of the present invention to provide an apparatus, wherein a pair of sonic receptors or vibrating plates relatively and separately receive original sounds, which are converted into output signals to respectively reproduce sounds really at the right and at the left from the original sounds of the right and left directions and to reproduce sounds really at the middle from the original sounds of the middle direction in order to achieve the effect of localization of sounds.

It is yet another object of the present invention to provide a compact and reliable microphone.

It is still yet another object of the present invention to provide a microphone constructed and arranged on the basis of the principle of Localization of Sounds.

With the above and other objects in view which will become apparent in the following detailed description, the present invention will be clearly understood in connection with theaccompanying drawing, in which:

FIGURE 1 is a diagram-matical sectional view of an essential portion of a novel microphone constructed in accordance with the present invention;

FIG. 2 is a diagram showing an electric circuit employed for an embodiment of the present invention; and

FIG. 3 is a fragmentary illustration of an electric circuit diagram of another embodiment of the present invention.

Referring now to the drawing, and more particularly to FIG. 1, the main structural portion of the present microphone consists, essentially, of a pair of protective grid electrode plates 4 and 4', a pair of vibratory plates or diaphragms 5 and 5 each of which is made of electrical conductor material, and a pair of grid electrode plates 7 and 7'. The protective grid electrode plates 4 and 4 are provided with insulating films or sheets P and P on their outer surface and also with a plurality of small openings 3 and 3, which are preferably of inverted frustoconical shape diverging outwardly.

The protective grid electrode plate 4 has an insulating bushing 2 disposed adjacent to both ends of the said plate 4, and the both ends of vibrating plate 5 are between insulating spacer rings 6. The grid electrode 7 is mounted on a mounting plate 9 by means of an insulating ring 8. A set screw 1 passes through appropriate tapped holes formed and aligned at each end of the above-mentioned members 2, 4, 5, 6, 7, 8 and 9, and is fastened at its lower end by a nut 10, to form a left sonic receptor unit or electrode-vibrating plate assembly. A right receptor unit or assembly substantially has the same construction as in the left unit, and therefore, any descriptions will be omitted in regard to the right unit except reference numerals with prime are attached to parts of the unit which correspond to those of the left unit.

The above-mentioned left and right sonic receptor units are pivotally interconnected with each other by a hinge C at the adjacent ends of the plates 9 and 9'. The interconnected electrode-vibratory plate assemblies are housed in a casing 11, thus forming a sound-absorbing chamber 12. An amplifying system 13 is positioned within the chamber 12.

The features of the invention are as follows. Each one of the electrode plates is disposed along each side of the vibratory plates. When voltages having opposite polarity are applied to the opposite plates 4 and 7 as well as 4' and 7' respectively as disclosed hereinafter, output signal voltages corresponding to the sounds from the central sources can be obtained from the pair of vibrating plates, and output signals from the left and right sound sources can be taken out of the left and the right opposite electrode plates, and thus, the ternary output signal voltages can be separately obtained at the same time from the original sounds carried from the right, center and left sources.

The opposite surfaces of the electrode plates 4 and 7, or 4 and 7 are cut out in an arcuate concave surface facing the vibrating plate therebetween in accordance with amplitude of the vibrating plates 5 or 5'. Thus spaces between the vibrating plate 5 or 5' and the electrode plates 4 and 7 or 4 and 7 can be relatively reduced in order to make the structure of the microphone compact, and at the same time, the vibrating plates are permitted to vibrate in a relatively large amplitude without touching the adjacent electrode plates and accordingly, large output signal voltages can be obtained.

As each protective grid electrode plates 4 and 4' is provided with the insulating film on its outer surface, it serves not only as the protective grid in a conventional microphone but also as electrode plate, thus improving the efficiency of the device. Further, because of a plurality of openings 3 and 3' of the specific shape as mentioned above on each plate 4 and 4, the area making sounds reflect is so decreased that substantial portion of sounds may be well guided to the vibrating plates. Furthermore, the openings converge toward the vibrating plate so as to possess small diameters on the side facing to the vibrating plate. As a result, remaining relatively large areas are available for electrode plate in relation to the vibrating plate.

Thus, when the plates 5 and 5' are vibrated by sound waves from the sources, relatively large output pulses may be obtained and the vibrating plate may be prevented from contacting with the electrode plates even during vibration in a large amplitude, so that the ternary or stereophonically arranged output signals can be efficiently taken out in a large scale without any distortion.

Further, the electrode plates 7 and 7 as well as mounting plates 9 and 9' have a plurality of apertures'as shown for guiding sounds, through which sound pressures from the vibrating plates are passed into and absorbed by the absorbing chamber 12. By adjusting the open angle of the central hinge C, it is possible to easily control the directional characteristics of the microphone.

When certain spatial sound sources to be picked up or reproduced are placed in the left, center and right directions with respect to the microphone, the central portion, i.e., portion having the hinge C, of the present microphone should be faced to the center of sound sources. Sound waves from the left direction will pass through the openings 3 in the left protective grid plate 4 and impinge upon the vibrating plate 5 to vibrate the same.

Referring now again to the drawing, and more particularly to FIG. 2, the left electrode plate 4 has a negative or cathode potential applied thereto from cathode side V of the power source through a resistor R3, and the left grid plate 7 has a positive or anode potential applied thereto through a resistor R1 from anode V+ of the power source. Consequently, the vibrating plate 5 is infiuenced on its each side by voltages having opposite polarities. It will be apparent from the above that the vibration of the plate 5 causes electrical changes according to the vibration. Thus voltage variations are relatively induced in the respective opposite electrode plates 4 and 7 in accordance with the motion of the vibrating plate 5 to produce substantially large signal voltages with little distortion, which signals, in order to be amplified, are connected through coupling capacitors C1 and C2 to grid of vacuum tubes V1 and V1, and grounded through grid resistances R5 and R6, respectively, thus producing signal L of the left side sounds at a left output transformer TL.

Sounds from the central sources pass evenly and equally through the openings 3 and 3 of plates 4 and 4' to vibrate the respective vibrating plates 5 and 5. A center point of a balance resistance RC is grounded in an appropriate manner so as to balance the induced voltages. As the vibrating plates 5 and 5 are positioned between the electrode plates with voltages of relatively opposite polarity applied thereto, sound waves from the center direction which vibrate the vibrating plates are converted into relatively large electrical signals at the respective ends of the balance resistance RC, the signals being obtained substantially without distortion and connected through coupling capacitors C3 and C4 to grids of vacuum tubes V2 and V2 in order to be amplified, and grounded by means of grid resistances R7 and R8. Thus, signal C of the sounds from the center sources are obtainable from a central output transformer TC.

Sounds from the right sources pass through the right openings 3 and impinge upon the plate 5 to vibrate the same. The right protective grid and electrode plate 4' have an anode voltage applied thereto from anode V,+ of the electrical source through resistor R2, and the grid electrode 7 has a cathode voltage applied thereto from cathode V of the electrical source through resistor R4, so that the opposite sides of the vibrating plate 5' are under the influence, respectively, of voltages having opposite polarities. When the plate 5' is vibrated, changes in voltage are respectively induced in the electrode plates to thereby produce relatively large signal voltages without distortion. In order to be amplified, the signal voltages are connected through coupling capacitors C5 and C6 to grids of vacuum tubes V3 and V3, and grounded by grid resistances R9 and R10, thus causing signal R corresponding to the sounds from the right source at a right output transformer TR.

In the illustrated embodiment, the reference characters, VB, R11 and C7 respectively designate a B-power supply for applying voltage to the plates of the vacuum tubes, a cathode resistance for providing bias voltage for each vacuum tube and a pass capacitor for the cathode.

Referring now again to the drawing, and more partic ularly to FIG. 3, there is illustrated another embodiment of the present invention, in which for the amplification of the signal voltages, transistors represented by T and T' (representing the left-hand tube portion of FIG. 2) are used in place of the vacuum tubes shown in FIG. 2, together with appropriate load resistances and bias battery (not shown). As will be apparent to those skilled in the art, various type transistors may alternatively be employed merely with minor changes in the electrical connections. Such a transistorized circuit permits the realization of a compact and solid assemblage of the stereophonic microphone according to the present invention.

It will be understood from the foregoing description that the present invention makes it possible to eificiently obtain stereophonic signals in accordance with a ternary arrangement in original sound sources.

By the localization-ofsound type microphone according to this invention, sounds received at the central portion can really be taken out of the central channel as electrical signals, and sounds at the left and right portion can really be taken out of the left and right channels. Therefore, the microphone system of this invention is superior in performance to the so-called stereo systems employed conventionally and can really achieve true stereophonic sound reproduction. The system of this invention can enjoy a wide range of application, such as, true stereophonic recording, stereophonic broadcasting and the like.

While I have disclosed several embodiments of the present invention, it is to be understood that these embodiments are given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claims.

I claim:

1. A stereophonic microphone, comprising a pair of sonic receptor means, each of which comprises two opposed electrode plate members and a vibrating plate member disposed between and closely spaced apart from said two opposed electrode plate members,

said two opposed electrode plate members in each of said pairs of sonic receptor means being adapted to have, respectively, voltages applied thereto of opposite polarity, and

said pair of sonic receptor means arranged so that sounds received between said pair of sonic receptor means induce in said vibrating plate members signal voltages representative of center sounds and sounds received at the right and left sonic receptor means induce in the right and left opposed electrode plate members, respectively, signal voltages representative of the right and left sounds to thereby provide true stereophonic signals to accomplish the effect of localization of sounds.

2. The stereophonic microphone, as set forth in claim 1, wherein said two opposed electrode plate members include an outer member and an inner member, and

one of said pair of sonic receptor means having its outer member adapted to have a negative potential applied thereto and its inner member adapted to have a positive potential applied thereto. 3. The stereophonic microphone, as set forth in claim 2, wherein the other of said pair of sonic receptor means having its outer member adapted to have a positive potential applied thereto and its inner member adapted to have a negative potential applied thereto. 4. The stereophonic microphone, as set forth in claim 1, wherein said two opposed electrode plate members in each of said pair of sonic receptor means include opposed surfaces, respectively, facing and spaced apart from said vibrating plate member and have arcuate concave surfaces facing said vibrating plate member, thereby increasing the space between said opposed surfaces and said vibrating plate member permitting an amplitude increase of the latter. 5. The stereophonic microphone, as set forth in claim 1, wherein said two opposed electrode plate members include an outer member, and said outer members in each of said pair of sonic receptor means are provided with a plurality of openings converging toward said vibrating plate member. 6. The stereophonic microphone, as set forth in claim 5 further comprising an insulating film material provided on the outer surface of said outer member but not on said plurality of openings. 7. The stereophonic microphone, as set forth in claim 5, wherein said two opposed electrode plate members include an inner member, and said inner members in each of said pair of sonic receptor means have openings formed therein for guiding and passing sound pressure from said vibrating plate members, respectively. 8. The stereophonic microphone, as set forth in claim 1, wherein said pair of sonic receptor means are pivotally interconnected at adjacent ends for controlling the directional characteristic of the microphone. 9. The stereophonic microphone, as set forth in claim 8, further comprising a casing in which said interconnected pair of sonic receptor means is accommodated, and said casing is semi-circular in section. 10. The stereophonic microphone, as set forth in claim 1, further comprising an electron tube circuit means for separately amplifying the right, center and left sound signal voltages, respectively. 11. The stereophonic microphone, as set forth in claim 1, further comprising a transistor circuit means for separately amplifying the right, center and left sound signal voltages, respectively.

References Cited UNITED STATES PATENTS 3,007,012 10/1961 Olson 179-111 3,184,550 5/1965 Rogers 179-13 KATHLEEN H. CLAFFY, Primary Examiner. RICHARD LINN, Assistant Examiner. 

